ASP.NET MVC FileContentResult IE 8.0 hangs on download

Question

some of my users are expieriencing problems when they try to download a report, the download just hangs on 0%, restarting IE usually fixes the problem.

why does this happen?

i am using ASP.NET MVC (v1), the my action looks like this

<Authorize()> _
<AcceptVerbs(HttpVerbs.Get)> _
Function RenderReport(ByVal guid As Guid, ByVal anonym As Boolean) As FileContentResult

    ...

    Dim mimeType As String = String.Empty
    Dim renderedBytes() As Byte = EmployeePresentation.Render(guid, mimeType, Server.MapPath("~/Reports/..."), anonym)
    Return File(renderedBytes, mimeType, filename)
End Function

the filename is US-ASCII encoded, filesize is usally around 300Kb, mimeType is application/pdf

tia